Tone Marking using Distinct Consonants
Orthographies that employ this form of tone marking are generally used in languages that developed tones from (usually voiced) consonants during their documented written history. Hence these tone-marking consonants were usually markers of voicing, and so it is debatable whether this truly counts as dedicated tone marking.
One good example is Lhasa Tibetan, which is written in an abugida generally held to have been developed in the 7th century CE. Modern Lhasa Tibetan is tonal, although the number of tones is subject to varying analyses. It is certain that there are at least 2, high and low; most analyses also split these, forming 4: high level, high falling, low level/slow-rising, low rising/rise-fall. Some even argue for 6, based on the slightly different contours of checked syllables from non-checked short vowels.
The following example shows how high falling vs low rising/rise-fall contrast with each other:
- ཕོད (Wylie: phod; IPA for Lhasa: /pʰøː˥˩/) = to dare
- འཕོད (Wylie: 'phod; Lhasa IPA: /pʰøː˥˩/) = completion
- བོད (Wylie: bod; IPA for Lhasa: /pʰøː˩˧˨/) = Tibet
- པོད (Wylie: pod; IPA for Lhasa: /pøː˥˩/) = book, volume
- འབོད (Wylie: 'bod; Lhasa IPA: /pøː˩˧˨/) = to call out, to shout
As can be seen from the Wylie transliteration, in Classical Tibetan the difference in the script encoded a three-way distinction between
པ voiceless plain /p/ ,
ཕ voiceless aspirated /pʰ/, and
བ voiced /b/.
With the diachronic devoicing that happened in most of medieval East and Southeast Asia, affecting specifically Central Tibetan including Lhasa, voiced consonants became voiceless aspirated + low tone, viz
བ = /pʰ/ + a low tone, creating the minimal pair
ཕ in the aspirated labial consonants. The same applies to the velar, palatal affricate, alveolar affricate, palatal/postalveolar fricative and alveolar fricative series.
Interestingly, this also extended to the unaspirated versions, because of the prefix consonant: the "a chung"
འ, whose phonetic realisation in Classical Tibetan is still under debate (either a voiced /ɦ/ or a nasal). It appears in the script either as the root consonant (directly bearing the vowel diacritic) or as a prefix to voiced or voiceless aspirated consonants, not voiceless plain consonants. In prefixed clusters with orthographic voiced consonants, this creates the contrast
འབ. Note that the a chung prefix does not form a contrast with orthographic aspirated consonants. Certain other consonants in prefix position like
ས also behave in this way.
- སྤོད (Wylie: spod, IPA: /pøː˥˩/) - spice/flavouring
- རྦོད (Wylie: rbod, IPA: /pøː˩˧˨/) - incite
The "secondary level" contrast between contours is much rarer, but this is still an example where the orthographic information is coded by a consonant, this time a final consonant. The quintessential example is:
- ཁམ (Wylie: kham, IPA for Lhasa: /kʰam˥/) [high level] - piece
- ཁམས (Wylie: khams, IPA for Lhasa: /kʰam˥˩/) [high falling] - Kham region of Tibet
These are examples of the few minimal pairs, ending in /m/ or /ŋ/, where short syllables are signalled with a final orthographic consonant after the sonorant.
Both the overall pitch level and the contour are encoded in orthographic consonant contrasts, that were likely originally pronounced as such in Classical Tibetan. Hence, the tone is a reflex of both lost voicing distinctions and a lost final segment. In some other Tibetan varieties, e.g. Amdo Tibetan, phonemic tones have not emerged and voicing is preserved in initial position.
A major example of a mixed use of consonants and tone diacritics to show tone is Thai. This abugida is well known for its rules for working out which orthographic elements map to the five tones of Central Thai. The 13th century Thai inscriptions do have tone markers as diacritics, but that was Old Thai, and with the various changes through time, modern Central Thai tone marking relies on three elements: 1) initial consonant; 2) tone diacritic; 3) final consonant, plus the mapping procedure.
Tone Marking Using Distinct Syllable Glyphs
The one that comes to my mind is Northern Yi (Nuosu) in the Modern Yi script, a syllabary standardised in 1975 although it dates back to the Tang dynasty. The language can be written in Roman script, with the post-syllable Roman glyphs -t, -x, null, or -p (generally listed in that order), but the modernised version of the traditional script is quite fascinating.
The -x tone (apparently mid falling or high-mid level in Liangshan Yi) is derived from the null (which is mid level), which reflects its marginal status in the language. However -t (high level tone) and -p (low falling tone) orthographic series do not necessarily have obvious parallels with the null series; although occasional resemblances can be gleaned for some finals (e.g. o with op) the majority are unrelated.
Tone Marking Using Positional Variants
This is a feature of the Pollard script, an abugida originally written for the Hmongic language of Northeastern Yunnan A-Hmao. The vowel itself is determined by the shape of the vowel diacritic, whilst its tone is determined by the position of the diacritic with respect to its base consonant. I see four tones are encoded by the script, although I haven't done much research into how the tones actually correspond.